Apparatus and method for electronically acquiring fingerprint images with low cost removable platen and separate imaging device

Abstract

A thin, inexpensive, removable platen for a direct fingerprint reader without a permanently attached platen. A removable platen is formed as a transparent area on a credit card, passport or identification card or as a separate card. The portable platen on the card is inserted over an imaging area of the direct fingerprint reader. Light from the direct fingerprint reader passes through an optical surface formed on the underside of the portable platen, is reflected off the fingerprint and passes back through the optical surface to the imaging apparatus where the image is digitized and analyzed. The optical surface is formed such that the incident light is not refracted away from the fingerprint and the reflected light from the fingerprint is not refracted away from the imaging apparatus.

Claims

1. An optical subsystem for a direct fingerprint reader, comprising:

a housing having an imaging aperture;

a light source for directing light toward said imaging aperture;

an imaging device for receiving light reflected from a fingertip or other portion of a body visible through said imaging aperture and electronically sensing the image in said reflected light;

a low cost, easily replaceable, disposable platen for placement in said imaging platen aperture and having a generally flat, thin configuration and having a first surface upon which a portion of a body such as a fingertip is placed when said platen is in use and a second surface which is generally parallel to said first surface and which includes a plurality of projections comprising an optical structure, said projections being small enough to maintain the generally flat, thin configuration of said disposable platen and comprised of material through which light can pass said plurality of projections of said optical structure having optical characteristics so as to function to prevent light rays originating at said light source arriving at said second surface from being reflected off said second surface toward said imaging device but instead causing said light rays to enter said disposable platen and travel through said disposable platen so as to reach said first surface without the need for guiding within the platen by total internal reflection, the shape of said first surface being such that the angle of incidence between light rays arriving at said first surface and a normal to said first surface is such that said light rays are refracted back toward said second surface from all portions of said first surface not in contact with flesh from the portion of body placed upon said first surface, and such that light rays arriving at portions of said first surface in contact with flesh of the portion of said body placed in contact with said first surface escape therefrom, the configuration of said projections being such that most light rays refracted toward said second surface from portions of said first surface not in contact with flesh exit said first surface and travel generally toward said imaging device.

2. The apparatus of claim 1 wherein said platen is comprised of plastic and wherein said projections of said optical structure comprise an array of parallel rows of microprisms each of which has an input surface having a normal pointing in a direction such that light arriving from said light source impinges on said first surface at portions thereof not in contact with flesh at an angle which is greater than the critical angle defined by Snell's law and are refracted toward said second surface but light which impinges on said first surface at portions thereof in contact with flesh impinge at an angle which is less than the critical angle defined by Snell's law such that these light rays escape said platen, each microprism also having an output surface having a normal pointing in a direction such that most light rays refracted from said first surface toward said second surface impinge upon said output surface at an angle which is less than the critical angle defined by Snell's law thereby escaping said platen and becoming available for imaging by said imaging device, and wherein the dimensions of each said microprism are such that said microprisms can be manufactured using stamping, pressure forming, injection molding or other processes substantially less expensive that semiconductor photolithography processes.

3. The apparatus of claim 1 wherein said disposable platen is made of plastic and wherein said plurality of projections have dimensions suitable for fabrication using pressure forming, stamping or injection molding.

4. The apparatus of claim 1 wherein said plurality of projections are triangular cross-section microprisms placed edge to edge at their bases in parallel rows across said second surface.

5. The apparatus of claim 4 wherein there are at least 50 parallel rows of microprisms per millimeter.

6. The apparatus of claim 1 manufactured by the process of stamping.

7. The apparatus of claim 1 manufactured by the process of injection molding.

8. A method of acquiring a working image of a fingerprint, comprising:

placing a portable, disposable fingerprint platen included as part of the structure of a credit card, identification card or passport on a direct fingerprint reader imaging device which does not have its own platen, said platen being generally flat and thin and of a size suitable for carrying in a wallet, and having an underside and a top side;

placing a finger or other portion of the body on said top side of said platen;

illuminating said underside of said portable fingerprint platen with a light source;

capturing the working image of the fingerprint in an imaging device from light rays reflected back into said direct fingerprint reader from said top side of said platen upon which the finger or other portion of the body was placed; and

using an optical structure on said underside of said platen, preventing reflection of non working light rays originating from said light source and travelling toward the underside of said platen which bear no fingerprint image information from being reflected from the underside of said platen toward said imaging device by refracting the rays first arriving from said light source at said underside so that the rays substantially all enter said platen and travel to said top side, said refraction at said underside being such that said light rays first arriving at said top side arrive at such an angle such that substantially all light rays which first arrive at portions of said top side in contact with flesh such as the ridges of a fingerprint exit said platen and escape whereas substantially all light rays which first arrive at portions of said top side which are not in contact with flesh such as the grooves of a fingerprint are refracted by the interface of said top side and the substance filling the grooves of said fingerprint back toward said underside, and preventing, at said underside, refraction or reflection away from said imaging device of light rays bearing fingerprint or other identification information which are first arriving at said underside after refraction from said top side.

9. A disposable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said disposable platen when said disposable platen is positioned in said fingerprint reader, comprising:

a thin, flat, light-transmitting, disposable platen having a a first surface upon which a finger or other portion of the body is to be placed when said disposable platen is placed in said fingerprint reader and a fingerprint is to be read, said platen having a second surface which is illuminated by light rays from said light source when said disposable platen is placed in said fingerprint reader said second surface having formed thereon a plurality of small microprisms which causes refraction of most of said light rays from said light source such that they pass through said second surface and propagate to said first surface at an angle relative to the normal of said first surface so as to be refracted from portions of said first surface not in contact with flesh back toward said second surface, said angle of said light rays arriving from said second surface relative to a normal to said first surface being such that most light rays which impinge upon portions of said first surface in contact with flesh escape therethrough thereby forming a working image, said second surface also being the surface through which light rays carrying said working image of said fingerprint passes enroute to said imaging device;

and wherein said said plurality of small microprisms on said second surface are formed in such as way such that a normal thereof points generally in the direction of said first surface and is oriented relative to the angle of arrival of said working ray refracted toward said second surface from said first surface such that most of said working rays pass through said second surface so that the image of the portion of the body in contact with said first surface may be detected by said imaging device.

10. A disposable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device, comprising:

a light transmitting generally flat, generally thin platen having a a first surface upon which a fingertip or other portion of the body is to be placed when said disposable platen is placed in said fingerprint reader and a fingerprint is to be read, and having a second surface illuminated by said light source when said disposable platen is placed in said fingerprint reader, said second surface being the surface through which light passes carrying an image of said fingerprint to said imaging device;

and wherein said second surface has formed thereon optical structure means for refracting light from said light source through said second surface toward said first surface such that said light arrives at said first surface without the need to be guided through said platen by total internal reflection, and arrives at said first surface at an angle relative to a normal to said first surface such that light rays impinging on portions of said first surface in contact with flesh escapes said platen while light rays that impinge upon said first surface not in contact with flesh are refracted back toward said second surface where said light rays arrive at an angle relative to a normal of a surface of said optical means such that most of said light rays escape said platen where they are focussed on said imaging device.

11. A disposable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device, comprising:

a thin, flat, light-transmitting, disposable platen having a first surface upon which a finger or other portion of the body is to be placed when said disposable platen is placed in said fingerprint reader and a fingerprint is to be read, said platen having a second surface which is illuminated by light rays from said light source when said disposable platen is placed in said fingerprint reader, said second surface having formed thereon a plurality of small microprisms which causes refraction of most of said light rays from said light source such that they pass through said second surface and propagate to said first surface at an angle relative to the normal of said first surface so as to be refracted from portions of said first surface not in contact with flesh back toward said second surface, said angle of said light rays arriving from said second surface relative to a normal to said first surface being such that most light rays which impinge upon portions of said first surface in contact with flesh escape therethrough thereby forming a working image, said second surface also being the surface through which light rays carrying said working image of said fingerprint passes enroute to said imaging device;

and wherein said said plurality of small microprisms on said second surface are formed in such as way such that a normal thereof is oriented relative to the angle of arrival of light refracted from said first surface toward said second surface such that most of said working rays pass through said second surface so as to make available to said imaging device the image of the portion of the body in contact with said first surface, and

wherein said platen has template data encoded thereon in a spatially distributed pattern of light and dark areas, said template data encoding the x, y and theta values of minutiae in the fingerprint of the rightful owner of the card.

12. A portable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said portable platen when said portable platen is positioned in said fingerprint reader, comprising:

a transparent plate having a a first surface upon which a finger is placed when said portable platen is placed in said fingerprint reader and a fingerprint is to be read, and having a second surface illuminated by said light source when said portable platen is placed in said fingerprint reader, and said second surface being the surface through which light carrying an image of said fingerprint passes enroute to said imaging device;

and wherein said second surface has formed thereon optical structures for preventing immediate reflection off said second surface toward said imaging device of nonworking light rays that originated from said light source and which are impinging on said second surface for the first time after being emitted from said light source and that bear no information about the working image of a fingerprint in contact with said first surface thereby preventing interference between non working light rays carrying no image information reflected from said second surface upon encountering said second surface for the first time after emission from said light source and working light rays carrying a working image of said fingerprint which are reflected from said first surface toward said imaging device and which pass through said second surface upon encountering said second surface for the first time after reflection from said first surface, said optical structures also for preventing reflection away from said imaging device at said second surface of working light rays carrying a working image of said fingerprint which are reflected from said first surface toward said imaging device and which are impinging on said second surface for the first time since reflection from said first surface, said optical structures being small enough to allow said transparent plate to be carried easily and comfortably in a wallet with other credit cards and identification cards,

and wherein said portable platen has template data encoded thereon in a spatially distributed pattern of light and dark areas said template data encoding the x, y and theta values of minutiae in the fingerprint of the rightful owner of the card,

and wherein said spatially distributed pattern of light and dark areas is a two dimensional barcode.

13. The apparatus of claim 12 wherein said template data is enciphered prior to encoding in said spatially distributed pattern of light and dark areas.

14. A portable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said portable platen when said portable platen is positioned in said fingerprint reader, comprising:

a transparent plate having an imaging surface upon which a finger is placed when said portable platen is placed in said fingerprint reader and a fingerprint is to be read, and having an undersurface illuminated by said light source when said portable platen is placed in said fingerprint reader, said undersurface being the surface through which light carrying an image of said fingerprint passes enroute to said imaging device;

and wherein said undersurface has formed thereon optical structures for preventing immediate reflection off said undersurface toward said imaging device of nonworking light rays that originated from said light source and which are impinging on said undersurface for the first time after being emitted from said light source and that bear no information about the working image of a fingerprint in contact with said first surface thereby preventing interference between nonworking light rays carrying no image information reflected from said undersurface upon encountering said undersurface for the first time after emission from said light source and working light rays carrying a working image of said fingerprint which are reflected from said imaging surface toward said imaging device and which pass through said undersurface upon encountering said undersurface for the first time after reflection from said imaging surface, said optical structures also for preventing reflection away from said imaging device at said undersurface of working light rays carrying a working image of said fingerprint which are reflected from said imaging surface toward said imaging device and which are impinging on said undersurface for the first time since reflection from said imaging surface, said optical structures being small enough to allow said transparent plate to be carried easily and comfortably in a wallet with other credit cards and identification cards, and

wherein said portable platen transparent plate is part of a credit card, identification card or passport, and

wherein said portable platen is configured for insertion into a direct fingerprint reader having an imaging aperture but no platen over said imaging aperture and having a light source which directs light toward said imaging aperture and having an optical path including an imaging device for receiving light from said imaging aperture and guiding said light to and focussing said light upon said imaging device, said transparent plate being positioned on said portable platen such that when said card is placed in said direct fingerprint reader, said transparent plate is located over said imaging aperture of said direct fingerprint reader, and wherein said optical structures comprise a plurality of microprisms each of which has a triangular cross-section having first and second faces, said first face having a normal which generally points at said light source and said second face having a normal which generally points at the region of said imaging surface upon which said finger or other portion of a body is placed.

15. The apparatus of claim 14 wherein each said microprism has an elongated shape with a long axis which extends all the way across said transparent portion of said portable platen and which is parallel to the long axis of each other microprism, said microprisms being placed edge to edge.

16. The apparatus of claim 15 wherein the density of said microprisms 50 microprisms per millimeter.

17. The apparatus of claim 16 wherein the imaging surface of said portable platen is coated with a transparent layer of rubber polyurethane.

18. The apparatus of claim 16 wherein the medium surrounding said portable platen when said card is placed in said direct fingerprint reader is air and wherein at each of said first and second faces of each microprism and at said imaging surface of said portable platen there is a critical angle defined by the Snell's law relationship ##EQU2## where n.sub.b =the index of refraction of the medium above the surface or face, and

n.sub.a =the index of refraction of the medium below the surface or face, and

.phi..sub.crit =the critical angle of total internal reflection wherein the angle of refraction is equal to 90.degree. such that the refracted light ray does not leave the medium it is travelling in but is refracted at an angle so as to travel parallel to said face or surface, and wherein the included angle between said first and second faces of each said microprism is such relative to the placement of said light source and said optical path that the angle of incidence of a light ray travelling from said light source toward said first face of said microprism when said light ray impinges on said first face of said microprism is less than said critical angle at said first face for light attempting to enter said transparent plate from said surrounding air thereby causing said light rays from said light source to enter said transparent plate and not be reflected or refracted away therefrom, and wherein the angle of incidence of a light ray refracted from said first face of said microprism on which it impinges is such that said light rays arriving at said imaging surface at locations thereof in contact with flesh arrive at less than the critical angle but also such that said light rays arriving at portions of said imaging surface in not in contact with flesh at an angle greater than the critical angle and are refracted toward a second face of a microprism such that when said light rays reach said second, the angle they arrive at is less than said critical angle for light travelling in said transparent plate and attempting to enter the surrounding air below said portable platen thereby causing said light rays to escape said transparent plate.

19. A portable platen for a direct electronic fingerprint reader, said reader having a light source and an imaging device located so as to be underneath said portable platen when said portable platen is positioned in said fingerprint reader, comprising:

a transparent plate having a a first surface upon which a finger is placed when said portable platen is placed in said fingerprint reader and a fingerprint is to be read, and having a second surface illuminated by said light source when said portable platen is placed in said fingerprint reader, said second surface being the surface through which light carrying an image of said fingerprint passes enroute to said imaging device;

and wherein said second surface has formed thereon optical structures for preventing immediate reflection off said second surface toward said imaging device of nonworking light rays that originated from said light source and which are impinging on said second surface for the first time after being emitted from said light source and that bear no information about the working image of a fingerprint in contact with said first surface thereby preventing interference between nonworking light rays carrying no image information reflected from said second surface upon encountering said second surface for the first time after emission from said light source and working light rays carrying a working image of said fingerprint which are reflected from said first surface toward said imaging device and which pass through said second surface upon encountering said second surface for the first time after reflection from said first surface, said optical structures also for preventing reflection away from said imaging device at said second surface of working light rays carrying a working image of said fingerprint which are reflected from said first surface toward said imaging device and which are impinging on said second surface for the first time since reflection from said first surface, said optical structures being small enough to allow said transparent plate to be carried easily and comfortably in a wallet with other credit cards and identification cards, and

wherein said portable platen transparent plate is part of a credit card, identification card or passport, and

wherein the medium surrounding said portable platen when said card is placed in said direct fingerprint reader is air and wherein at each of said first and second surfaces there is a critical angle defined by the relationship ##EQU3## where n.sub.b =the index of refraction of the medium above the surface, and

n.sub.a =the index of refraction of the medium below the surface, and

.phi..sub.crit =the critical angle of total internal reflection wherein the angle of refraction is equal to 90.degree. such that the refracted ray does not leave the medium it is travelling in but is refracted at an angle so as to travel parallel to said surface, and wherein said optical means has first and second portions, said first portion having light from said light source incident thereon and said second portion having light refracted from said first surface incident thereon, and wherein the orientation and shape of said first and second portions relative to the placement of said light source and said optical path is such that the angle of incidence of a light ray travelling from said light source toward said first portion when said light ray impinges on said first portion is less than said critical angle at said first portion for light attempting to enter said transparent plate from said surrounding air, and wherein the angle of incidence of a light ray refracted from said first surface of said transparent plate toward second portion when said light ray reaches said second portion is less than said critical angle for light travelling in said transparent plate and attempting to enter the surrounding air.

20. A method of using a direct fingerprint reader having an illumination light source and having an imaging device for capturing an image of a fingerprint or some other identifying feature of the body of the user, said direct fingerprint reader being without a platen, comprising carrying a personal platen on the person of a user and placing said personal platen on said fingerprint reader so as to be illuminated by said light source, placing a portion of the body of said user on the platen to be imaged by said direct fingerprint reader, and wherein said personal platen has a first surface in contact with said portion of the body of said user to be identified and a second surface illuminated by a light source, said personal platen carrying out the steps of receiving light from a light source and refracting most of said received light such that it enters said platen and propagates toward said first surface without the need for guiding within said platen by total internal reflection and such that said refracted light arrives at said first surface at an angle such that light rays which impinge on said first surface at portions thereof not in contact with flesh impinge at an angle which is greater than the critical angle defined by Snell's law and are refracted toward said second surface, but light rays which impinge on said first surface at portions thereof in contact with flesh impinge at an angle which is less than the critical angle defined by Snell's law such that these light rays escape said platen, said platen also receiving said light rays refracted toward said second surface from said first surface and refracting them at said second surface such that most thereof exit said platen, and capturing at least some of said light rays which exit said platen at said second surface using said imaging device.

21. A method of using a direct fingerprint reader having an illumination light source and having an imaging device for capturing an image of a fingerprint or some other identifying feature of the body of the user, said direct fingerprint reader being without a platen comprising: carrying a personal platen on the person of a user and placing said personal platen on said fingerprint reader so as to be illuminated by said light source, and placing a portion of the body of said user on the platen to be imaged by said direct fingerprint reader, and preventing interference between working light rays that carry an image of an identifying feature of a user's body and non working rays which carry no such image data by preventing reflection toward said imaging device of non working light rays originating from said light source and travelling toward the underside of said personal platen which, after reflection from said underside of said platen, would bear no image information, and preventing reflection of working light rays bearing image information regarding said identifying feature of the body of the user away from said imaging device at the underside of said platen, and further comprising the step of removing said personal platen after use and carrying said personal platen on the person of the user.

22. A method of using a direct fingerprint reader having an illumination light source and having an imaging device for capturing an image of a fingerprint or some other identifying feature of the body of the user, said direct fingerprint reader being without a platen comprising carrying a personal platen on the person of a user and placing said personal platen on said fingerprint reader so as to be illuminated by said light source, and placing a portion of the body of said user on the platen to be imaged by said direct fingerprint reader, and preventing interference between working light rays that carry an image of an identifying feature of a user's body and non working rays which carry no such image data by preventing reflection toward said imaging device of non working light rays originating from said light source and travelling toward the underside of said personal platen which, after reflection from said underside of said platen, would bear no image information, and preventing reflection of working light rays bearing image information regarding said identifying feature of the body of the user away from said imaging device at the underside of said platen, and wherein said personal platen is placed on said direct fingerprint reader by placing a credit card on said direct fingerprint reader, said credit card having said personal platen incorporated therein, and wherein the image of the fingerprint developed using said personal platen is used to verify the identity of the user for purposes of authorizing transactions using said credit card.

23. A method of using a direct fingerprint reader having an illumination light source and having an imaging device for capturing an image of a fingerprint or some other identifying feature of the body of the user, said direct fingerprint reader being without a platen comprising carrying a personal platen on the person of a user and placing said personal platen on said fingerprint reader so as to be illuminated by said light source, and placing a portion of the body of said user on the platen to be imaged by said direct fingerprint reader, and preventing interference between working light rays that carry an image of an identifying feature of a user's body and non working rays which carry no such image data by preventing reflection toward said imaging device of non working light rays originating from said light source and travelling toward the underside of said personal platen which, after reflection from said underside of said platen, would bear no image information, and preventing reflection of working light rays bearing image information regarding said identifying feature of the body of the user away from said imaging device at the underside of said platen, and further comprising the step of discarding said platen after placing said personal platen on said direct fingerprint reader.

24. A personal platen embodied in a credit card and having a light transmitting imaging surface of one surface of said credit card upon which a fingertip or other portion of the body is placed and having an undersurface which is illuminated by a light source when said personal platen is placed in a direct fingerprint reader, said personal platen being made of plastic, said undersurface having optical structures thereo that modify the light reflecting and refracting properties of said undersurface such that light arriving at said undersurface is refracted such that a high percentage of said light rays arriving said light source enter said personal platen and few light rays arriving at said undersurface are reflected or refracted at said undersurface toward said imaging device in said direct fingerprint reader in which said personal platen is located, said light rays which enter said personal platen propagating therein to said imaging surface without the need for light waveguide type total internal reflection to guide said light rays to said imaging surface, said light rays which enter said platen being refracted at said undersurface in such a way that said light rays which enter said platen arrives at portions of said imaging surface not in contact with flesh at an angle greater than the critical angle defined by Snell's law and are refracted at said imaging surface back toward said undersurface, and said light rays which enter said platen being refracted at said undersurface in such a way that said light rays arriving at portions of said imaging surface in contact with flesh arrive at an angle which is less than the critical angle defined by Snell's law and exit said platen at said imaging surface, said optical structures being configured to also modify the optical properties of said undersurface such that most light rays refracted by said imaging surface toward said undersurface arrives at said undersurface at an angle which is less than the critical angle defined by Snell's law and exit said platen.

25. A personal platen embodied in a credit card and having a light transmitting imaging surface on one surface of said credit card upon which no information is encoded and upon which a fingertip is placed and having an undersurface meant for illumination on the opposite side of said credit card, said personal platen being made of light transmitting plastic, said undersurface characterized by optical structures that modify the light reflecting properties of said undersurface such that interference between working light rays carrying a fingerprint image reflected from said imaging surface and non working light rays that carry no image information that would be reflected from said undersurface if said optical structures were not present does not occur, said optical structures also modifying the light reflecting properties of said undersurface such that working light rays carrying said fingerprint image are not reflected back toward said imaging surface by said undersurface, and wherein said optical structures comprise an array of very small structures which do not appreciably derogate from the generally flat, thin shape of said credit card and each of which has a first surface which is illuminated by a light source when fingerprint imaging is occurring, said first surface having a normal which points in a direction such that light arriving at said first surface from said light source impinges thereon at an incidence angle which is less than the critical angle, each said optical structure also having a second surface through which passes working light rays carrying an image of a fingerprint, said second surface having a normal pointing in a direction such that said working light rays impinge on said second surface at less than the critical angle.

26. The personal platen of claim 25 wherein said optical structures are formed by a process selected from the group comprised of heat stamping and injection molding.

27. A fingerprint imaging system, comprising:

an electronic fingerprint reader having a receiver for receiving a card but lacking a platen upon which a fingertip or other portion of the body of a user is placed but having an imaging aperture within said receiver which is illuminated by light from a light source and having an imaging device which captures light reflected by a portion of a users body visible in said imaging aperture; and

a card small enough to be carried by a user and having formed therein a personal platen portion having an imaging surface and an undersurface, said card being made of plastic and sized to fit within said receiver of said fingerprint reader, and said personal platen portion formed in said card so as to be over said imaging aperture of said fingerprint reader when said card is placed in the receiver thereof, said personal platen portion being light transmissive at all locations within the perimeter of said imaging aperture and having no information recorded thereon, said card having optical structure means formed on said undersurface of said personal platen portion for altering the light reflecting and refracting properties of said undersurface such that light rays from said light source arriving at said undersurface are refracted such that a high percentage of said light rays enter said personal platen and few light rays arriving at said undersurface are reflected or refracted at said undersurface toward said imaging device, said light rays which enter said personal platen propagating therein to said imaging surface without the need for light waveguide type total internal reflection to guide said light rays to said imaging surface, light rays being refracted at said undersurface in such a way that said light rays which enter said platen and arrive at portions of said imaging surface not in contact with flesh arrive at an angle greater than the critical angle defined by Snell's law and are refracted at said imaging surface back toward said undersurface, and such that said light rays which enter said platen are refracted at said undersurface in such a way that said light rays which enter said platen arrive at portions of said imaging surface in contact with flesh at an angle which is less than the critical angle defined by Snell's law and exit said platen at said imaging surface, said optical structures being configured to also modify the optical properties of said undersurface such that most light rays refracted by said imaging surface toward said undersurface arrives at said undersurface at an angle which is less than the critical angle defined by Snell's law and exit said platen.

28. A fingerprint imaging system for capturing an image of a fingerprint, comprising:

a removable, disposable, substantially flat, substantially thin personal platen made of plastic and having dimensions suitable for carrying in a wallet, and having an imaging surface which is completely transparent and upon which is placed a finger or other portion of the body of a user when the fingerprint image or other identifying characteristics of that user to be imaged, and an undersurface having optical structures thereon designed to modify the light reflecting properties of said illumination surface such that light arriving at said undersurface is refracted such that a high percentage of said light rays arriving said light source enter said personal platen and few light rays arriving at said undersurface are reflected or refracted at said undersurface toward said imaging device in said direct fingerprint reader in which said personal platen is located, said light rays which enter said personal platen propagating therein to said imaging surface without the need for light waveguide type total internal reflection to guide said light rays to said imaging surface, said light rays which enter said platen being refracted at said undersurface in such a way that said light rays which enter said platen arrives at portions of said imaging surface not in contact with flesh at an angle greater than the critical angle defined by Snell's law and are refracted at said imaging surface back toward said undersurface, and said light rays which enter said platen being refracted at said undersurface in such a way that said light rays arriving at portions of said imaging surface in contact with flesh arrive at an angle which is less than the critical angle defined by Snell's law and exit said platen at said imaging surface, said optical structures being configured to also modify the optical properties of said undersurface such that most light rays refracted by said imaging surface toward said undersurface arrives at said undersurface at an angle which is less than the critical angle defined by Snell's law and exit said platen, said optical structures being small enough such that they do not substantially alter the generally flat configuration of said card but not so small that they cannot be manufactured by pressure forming, stamping or injection molding;

a direct fingerprint imaging apparatus for receiving said removable platen, said direct fingerprint imaging apparatus including a light source for illuminating said undersurface and including an imaging device for capturing an image.

29. The apparatus of claim 28 wherein said removable personal platen is embodied in a credit card at the location where a user would normally grasp the card to place it in said direct fingerprint imaging apparatus.

30. The apparatus of claim 29 wherein said credit card includes information about the user encoded thereon.

31. The apparatus of claim 29 wherein said credit card has encoded therein information about the user and indicia information about the user's authorized fingerprint.

32. A fingerprint imaging system for capturing an image of a fingerprint, comprising:

a removable, disposable personal platen having an imaging surface upon which is placed a finger or other portion of the body of a user when the fingerprint or other identifying characteristic of a portion of the body of that user is to be imaged, and an undersurface having optical structures thereon designed to modify the light reflecting and refracting properties of said undersurface;

a direct fingerprint imaging apparatus for receiving said removable, disposable platen, said direct fingerprint imaging apparatus including a light source for illuminating said undersurface and including an imaging device for capturing an image of said fingerprint; and wherein said optical structures modify the optical properties of said undersurface such that light rays from said light source arriving at said undersurface are refracted such that a high percentage of said light rays enter said personal platen and few light rays arriving at said undersurface from said light source are reflected or refracted at said undersurface toward said imaging device, said light rays which enter said personal platen propagating therein to said imaging surface without the need for light waveguide type total internal reflection to guide said light rays to said imaging surface, light rays which enter said platen being refracted at said undersurface in such a way that said light rays which enter said platen arrive at portions of said imaging surface not in contact with flesh at an angle greater than the critical angle defined by Snell's law and are refracted at said imaging surface back toward said undersurface, and said light rays which enter said platen being refracted at said undersurface in such a way that said light rays arrive at portions of said imaging surface in contact with flesh at an angle which is less than the critical angle defined by Snell's law and exit said platen at said imaging surface, said optical structures being configured to also modify the optical properties of said undersurface such that most light rays refracted by said imaging surface toward said undersurface arrive at said undersurface at an angle which is less than the critical angle defined by Snell's law and exit said platen.

33. The apparatus of claim 32 wherein said imaging surface is large enough to use for either flat or rolled images of a fingerprint.

34. The apparatus of claim 32 wherein said imaging surface is large enough to use for capturing an image of palms or feet.

35. The apparatus of claim 32 wherein said optical structures comprises a plurality of small, adjacent prisms arranged into an array and which are small enough so that the platen has a generally flat configuration but are not so small that they cannot be manufactured using pressure forming, stamping or injection molding.

36. The apparatus of claim 32 wherein said optical structures comprise a diffraction grating.

37. The apparatus of claim 32 wherein said imaging surface includes a coating that improves optical contact between the portion of the user's body placed thereon and said platen.

38. The apparatus of claim 32 wherein said removable personal platen has encoded therein demographic information about the user and the user's authorized fingerprint and wherein said information about said user is encoded in the form of an image which can be detected by said imaging means.

39. The apparatus of claim 32 wherein said platen has encoded therein information about the user and the user's authorized fingerprint including fingerprint indicia data which can be used to compare with fingerprint indicia data developed by said direct fingerprint imaging apparatus from said fingerprint image detected using said removable personal platen, and wherein said information is encoded in the form of an image which can be detected by said imaging means when illuminated by a different light source than that used to detect said fingerprint image.

40. A fingerprint imaging system for capturing an image of a fingerprint, comprising:

a removable personal platen having an imaging surface upon which is placed a finger of a user when the fingerprint image of that user is to be captured, and an illumination surface having optical structure means for modifying the light reflecting properties of said illumination surface so as to prevent interference between working light rays reflected from said imaging surface bearing said fingerprint image and non working light rays reflected off said illumination surface and which bear no fingerprint image information, said optical structures being small enough so as to not interfere with the ability to easily fit said removable personal platen in a wallet;

a direct fingerprint imaging apparatus for receiving said removable platen, said direct fingerprint imaging apparatus including a light source for illuminating said illumination surface and including imaging means for capturing an image of said fingerprint; and

wherein said direct fingerprint imaging apparatus includes a transparent dust protector cover having a first portion oriented so as to be at right angles to said rays from said light source and a second portion between said imaging surface and said imaging means and oriented at right angles to the rays reflected from said imaging surface, said dust protector cover for preventing dust from collecting on said light source or said imaging means.

41. The apparatus of claim 40 wherein said second portion of said dust protector cover is within the focal length of said camera means and does not serve as an optical component.

42. The apparatus of claim 41 further comprising an additional protective cover which is movable on tracks between a first position wherein the imaging means and light source are protected from exposure to light from the ambient and a second position wherein said removable personal platen may be placed on said direct fingerprint imaging apparatus.

43. The apparatus of claim 42 wherein said direct fingerprint imaging apparatus includes a slot into which said removable personal platen is placed and futher comprising a sensor apparatus for sensing the presence of a personal platen in said slot and for automatically retracting said protective cover to said second position.

44. The apparatus of claim 43 wherein said sensor apparatus includes apparatus for receiving a signal from said direct fingerprint imaging apparatus that indicates when said removable personal platen is a valid card based upon reading of magnetically recorded information on said card, and does not retract said protective cover unless said signal indicates said card is valid.

45. A portable platen for a direct electronic fingerprint reader, said reader having a light source located so as to be able to illuminate the surface of a finger or other body part through said portable platen and an imaging device located so as to be focussed on a finger or other body part through said portable platen when said portable platen is positioned in said fingerprint reader, comprising:

a substantially flat, thin, disposable plastic card which is transparent or semitransparent at the frequency of light emitted from said light source, said card having a first surface upon which a finger or other body part is placed when said card is placed in said fingerprint reader and a fingerprint or other body part is to be imaged, and having a second surface which is illuminated by said light source when said card is placed in said fingerprint reader, said second surface being the surface through which light carrying an image of said fingerprint or other body part passes enroute to said imaging device;

and wherein said second surface has formed thereon an optical structure which alters the optical properties of said second surface such that light rays from said light source arriving at said second surface are refracted such that a high percentage of said light rays enter said card and few light rays arriving at said second surface from said light source are reflected or refracted at said second surface toward said imaging device, said light rays which enter said card propagating therein to said first surface without the need for light waveguide type total internal reflection to guide said light rays to said first surface, light rays which enter said card being refracted at said second surface in such a way that said light rays which enter said platen arrive at portions of said first surface not in contact with flesh at an angle greater than the critical angle defined by Snell's law and are refracted at said first surface back toward said second surface, and said light rays which enter said card being refracted at said second surface in such a way that said light rays arrive at portions of said first surface in contact with flesh at an angle which is less than the critical angle defined by Snell's law and exit said platen at said first surface, said optical structures being configured to also modify the optical properties of said second surface such that most light rays refracted by said first surface toward said second surface arrive at said second surface at an angle which is less than the critical angle defined by Snell's law and exit said platen;

and wherein said optical structures are an array of parallel rows of triangular cross-section microprisms placed base to base and a pitch of at least 50 rows per millimeter with an included angle at the tip of each triangular shaped prism being selected to provide the modifications of the optical properties of said second surface stated herein.